Set `authentication_method` on kafka listener

[vuldin]

There’s currently no option to set authentication_method on the Kafka listener. I hard-coded this into the defaults.j2 for the time-being. Could this be made into a variable that can be toggled if SASL is enabled or is there another way to achieve the same?

      "kafka_api": [
        {
          "address": "{{ hostvars[inventory_hostname].private_ip }}",
          "port": "{{ redpanda_kafka_port }}",
          "authentication_method": "sasl"
        }
      ],

[gene-redpanda]

SASL specifically is part of a larger issue that needs to be returned to. Per host overrides are in though and I hope that that fixes this issue for now. Setting auth method specifically -- as opposed to overriding the listener -- I am not a big fan of as particular auth methods tend to need supporting stuff on other listeners/in redpanda that can't be captured by an individual entry.